One (1) in every 6 American men will be diagnosed with prostate cancer over the course of their lifetimes, with 31,000 dying each year from the disease. Therapy for locally advanced disease remains contentious and an increasing number of options are available. More accurate staging would facilitate treatment decisions and lead to a better outcome for patients. In particularly dire need is a way to detect small lesions, i.e., recurrent tumors in the surgical bed, local lymph node invasion and other subtle manifestations of the disease in men with an elevated serum prostate specific antigen (PSA) but no other obvious symptoms. The current standard of PCa staging is shifting. Metabolic imaging techniques such as magnetic resonance spectroscopy (MRS), positron emission tomography (PET) and single photon emission computed tomography (SPECT) are gaining favor over the anatomic techniques of computed tomography (CT) and MR, which merely detect enlarged tissue, revealing nothing of its underlying physiology. In particular, SPECT using the radiolabeled monoclonal antibody (mAb) 1111n-capromab pendetide (Cyt-356, ProstaScint) is beginning to show promise in the clinic for identifying candidates for salvage radiotherapy. ProstaScint takes advantage of binding to the prostate specific membrane antigen (PSMA), a cell surface protein that has enzymatic activity and is becoming increasingly recognized as an important prognostic factor and marker of androgen-independent disease. Because of the well-known complexity of obtaining and interpreting ProstaScint images as well as the inherently difficult pharmacokinetics of antibody-mediated imaging and therapy, we have embarked upon a program that focuses on the development of small molecule probes for PSMA-based PCa imaging. Those probes are based on our initial success in synthesizing inhibitors of glutamate carboxypeptidase II (GCPII, a.k.a. N-acetylated-a-linked acidic dipeptidase or NAALADase) because PSMA possesses glutamate carboxypeptidase activity and has a nearly identical pharmacological and molecular profile to GCPII. Although we have achieved the fundamentals of success with regard to a new PET-based imaging agent for PCa in this fashion, we intend to expand upon that by synthesizing several new SPECT radiopharmaceuticals and testing them using the X-SPECT small animal imaging system. [unreadable] [unreadable]